The conventional methods of controlling inductive current in especially proportional solenoid valves as well as in inductive switch gear apparatus are well known in the art.
The use of controllers, and/or two-position controllers for alternately transmitting full operating load current and then zero current into the coil of the solenoid valve is shown and disclosed in European patent EP-PS 0 008 509. By interchanging the switching relationship, the average current can be effectively controlled from a zero level to a maximum value.
In order to protect the transistors in the electrical equipment against the inductive current surges during shut-down or opening of the circuit, it is to provide suppressing means to handle the inductive kick such as, using a forward biased conducting diode. Such an arrangement has the advantage that the magnetic field decay of the inductive surge remains stable during inactive operation. The electrical power required for such inductive spikes can be held to relatively small value.
Utilization of a forward biased diode becomes disadvantageous, when the activated solenoid valve is to react rapidly, as the diode impedes the rapid reduction of the magnetic field. It is known from the above patent, that the inductive surge of the circuit can be reduced rapidly by means of a Zener diode. Attention must be paid to the fact that the generated switch-off voltage does not exceed a given value since the switching transistor can be damaged by excess voltage.
The above arrangements may be used for a controlling solenoid valve of a fuel injection system. In this case, only an ON and OFF operation is necessary or required since an injector valve is either fully opened or fully closed.